1. Field of the Invention
The present invention relates to a power transmission for automotive vehicles, and more particularly to a power transfer device for four-wheel drive in combination with a power transmission.
2. Discussion of the Background
In copending U.S. patent application No. 795,862, filed on Nov. 5, 1985, now U.S. Pat. No. 4,645,029, there has been proposed a power transfer device for four-wheel drive in combination with a power transmission, which comprises a transfer casing detachably secured at one side thereof to a transmission casing, a first differential gear unit rotatably mounted within the transmission casing and having an input member in the form of a gear casing drivingly connected to an output gear of the transmission to split the driving power from the transmission into two torque delivery paths respectively for front-wheel drive and rear-wheel drive, a second differential gear unit arranged coaxially with the first differential gear unit and having an input member in the form of a gear casing integral with an output element of the first differential gear unit and rotatably mounted within the gear casing of the first differential gear unit, a carrier member rotatably mounted within the transfer casing and arranged coaxially with the first and second differential gear units, a first wheel axle drivingly connected to the inner end thereof with an output element of the second differential gear unit and extending outwardly from the transmission casing, a second wheel axle drivingly connected at the inner end thereof with another output element of the second differential gear unit and extending outwardly from the transfer casing through the carrier member, a hollow shaft arranged in surrounding relationship with the second wheel axle and having one end integral with another output element of the first differential gear unit and another end connected with the carrier member, and a clutch sleeve arranged between the first differential gear unit and the carrier member and axially slidably mounted on the hollow shaft by means of a spline connection to be selectively engaged with the input gear casing of the first differential gear unit.
During assembly process of the power transfer device, the first and second differential gear units are previously assembled within the transmission casing, while the carrier member and clutch sleeve are also previously assembled within the transfer casing. Thereafter, the transfer casing is fitted at its one end seating face to the transmission casing in such a manner that the carrier member and clutch sleeve are coupled over the hollow shaft. At this assembly step, it is difficult to carry the clutch sleeve in place for coupling over the hollow shaft, and it is also difficult to position the clutch sleeve for eliminating phase shift between the internal splines of the clutch sleeve and the external splines of the hollow shaft, if any. For this reason, if there is phase shift between the internal splines of the clutch sleeve and the external splines of the hollow shaft at the assembly step, it will be disable to couple the clutch sleeve over the hollow shaft. In such a situation, the transfer casing must be moved to effect coupling of the clutch sleeve with the hollow shaft.